Medical retrieval devices generally are used to retrieve biological and foreign material including stones from the body. Such medical retrieval devices may be used through an endoscope or a laparoscope.
One type of known medical retrieval device has a sheath and a retrieval assembly such as a basket that is movable in and out of the sheath. When the basket is within the sheath, the basket assumes a collapsed, reduced diameter profile. When the sheath is retracted relative to the basket or the basket is moved beyond the end of the sheath, the basket expands to a relatively larger diameter than when the basket is enclosed within the sheath.
With many known retrieval devices, materials are used in the retrieval assembly to enhance its rigidity. However, rigid materials used to enhance strength do so at the expense of flexibility. Moreover, rigid materials used in present retrieval assemblies have a fixed degree of flexibility and rigidity that cannot be altered to the conditions in which the retrieval assembly is used. The retrieval assembly must, on the one hand, be sufficiently strong to dilate the body tract and, on the other hand, be sufficiently flexible to negotiate body tracts having small diameters, tortuous pathways, and irregular lumens. Flexible retrieval assemblies can more easily capture large stones through the gaps in the legs of the retrieval assembly, than can rigid retrieval assemblies. When flexible materials are used in the retrieval assembly, however, rigidity and strength are compromised.
Also, in existing medical retrieval baskets, the contour of the baskets generally is round, oval, or pear-shaped, and the baskets are formed by a plurality of legs. Stones or other biological materials are captured in the basket by moving the basket around the material to be retrieved and maneuvering the material into the basket through the space between the basket legs.
After the material is captured in the basket, it is generally difficult to release the material from the basket if release of the captured material is required or indicated. The technical difficulty in releasing material such as a captured stone is a characteristic of known medical retrieval baskets in general. In some patients with long-standing clinical problems with urinary tract stones, a cicatrix may form in the tract as a result of trauma to its lining. The stenosis created by the cicatrix may not be so narrow so as to interfere with insertion of a retrieval basket while the basket is in a closed position. However, after the basket is expanded to capture the stone that is lodged beyond the stenotic area of the tract, the diameter of the basket containing the captured stone may exceed the diameter of the stenotic region of the urinary tract. Under these circumstances, release of the stone from the basket is a prerequisite for withdrawal of the device from the urinary tract. If the stone cannot be released, more invasive, surgical approaches are required to disengage the stone from the basket.
Improved devices and methods for retrieving material from a body are, therefore, needed.